The ability to make decisions based on abstract categories is a fundamental component of higher-order cognition and is essential for survival. In the past decade, much progress in understanding categorical decision-making has been made through the combination of visual psychophysics and single-unit neurophysiology in awake, behaving monkeys. This work has led to a clearer understanding of decision networks in parietal, frontal and inferotemporal cortex. However, two very basic questions remain unresolved. First, how does activity in specific brain regions targeted by single unit studies relate to the overall pattern of brain activation when monkeys are engaged in decision-making tasks? What additional regions also are involved in processing such decisions, and what role do such regions play? Second, are results from non-human primates applicable to humans? Specifically, given identical psychophysical tasks, can we establish functional homology between human and non-human primate brains? To answer these questions, we propose to use functional magnetic resonance imaging in awake behaving monkeys to map brain regions that are activated during a perceptual categorization task, using a paradigm identical to one used with human subjects. The proposed experiments will open up a new avenue of research into cognitive processes that are dramatically impaired in schizophrenia, attention-deficit disorder, Parkinson's disease, and Alzheimer's disease. [unreadable] [unreadable] [unreadable]